It's not everybody who can claim to have been picked up by Jamie Lee Curtis, but it happened to me. The fact that the pick-up merely involved being given a lift on a golf buggy should not, I believe, detract from the essential glamour of the occasion; nor, indeed, should the additional presence of diminutive monologist Ronnie Corbett. Quite the reverse, in fact.

They're here, a few miles from the film's Pinewood base, to shoot one of the concluding scenes of Fierce Creatures, the follow-up ("not so much a sequel as an equal") to A Fish Called Wanda, which reunites the original cast of Curtis, John Cleese, Michael Palin and Kevin Kline and augments it with a fine selection of great British comic actors such as Corbett and Robert Lindsay.

So successful was Kline in Wanda - he won an Oscar for Best Supporting Actor for his role as Otto, the deranged Nietzschean thief - that this time round, Cleese and co-author Iain Johnstone have written him two parts, as a father/ son team of antipodean tycoon grotesques bent on asset-stripping a small British zoo. In the scene currently being shot, Kline the elder is chasing his errant helicopter across a field, only to realise - too late! - that he has stumbled into the enclosure of the zoo's angry rhino. In a suitably grisly end, the tycoon gets trampled to death by an animatronic rhino. Cut!

Designed to add a little moral fibre to the earlier film's Ealing-style larks, Fierce Creatures presents a David and Goliath-style confrontation between the forces of good - the zoo's keepers - and the forces of unfeeling global corporatism, who try to impose sponsorship and a "fierce creatures only" theme on the zoo, in a (misguided) attempt to maximise profits. It's rather like The Titfield Thunderbolt; although with animals in place of steam engines, and is just as replete with whimsical British rusticity of the warm-beer, village-green cricket-match type so beloved of our present PM.

As with the huge zoo set constructed on the backlot at Pinewood, this location is festooned with sponsors' logos, one of the younger Kline's more stupid ideas. Huge photos announce the involvement of stars such as Kevin Costner and Bruce Springsteen in sponsoring certain animal enclosures, and the zoo's gorilla, Gordon, even has his name picked out in the requisite gin-related typeface. It's satire heavy-handed enough to click with even the dullest of American audiences, just as the cute little ring-tailed lemur chosen as the main marketing image leaves one in little doubt as to the film-makers' stance on animal cruelty. In theory, at least.

"Kill the little bastards! Swat them!" Cleese cries suddenly, waving his wide-brimmed hat frantically around him. The former Python's animal sympathies have been sorely tested, apparently, by a swarm of wasps which have plagued the set for the past few days. "They say you shouldn't annoy them, you should leave them alone and they'll not sting you, but it's not true. Just swat the bastards!"

Back in his trailer, away from the insect squadrons, Cleese calms down enough for a chat. Surely, I ask, he's aware of the old thespian dictum about never working with children or animals?

"Apparently," he corrects me, "the original version of that, in the 1950s, was: Never work with children, animals or Stewart Granger! But the animals have actually performed extraordinarily well, with the particular exception of an animal called a Patagonian Mara, which we all hate, because it only has two modes of operation - one is coma and the other is panic. Rather like one of my recent wives, actually."

The huge success of A Fish Called Wanda, he claims, brought no undue pressure to come up with a sequel. "The only pressure is that I can walk into a Hollywood studio and say to them, 'I would like to make a movie and it's not a huge sum of money and it's probably going to be funny, are you interested?', knowing they'll probably say 'yes'. That's hardly pressure."

Once the project started, however, Cleese became acutely aware of the increased level of expectation riding on the film. "It's rather like the second series of Fawlty Towers, which, in some ways, I didn't enjoy anything like as much as the first, because when the expectations are higher, you're much more likely to fail. But the hardest thing in the world is to make a really satisfying comedy. I know we've made a film with several funny things in it, but whether it will all come together and make a satisfying whole is something I'll probably begin to know in about 10 weeks, when we show it to our first audience."

For Wanda, there were apparently 12 such screenings, with re-edits after each showing. This time, Cleese expected no less, anticipating a constant process of feedback and fix until he and director Robert Young had something they wouldn't be ashamed to take to an American screening. "Then, after that screening, we'll know whether we're in trouble and need re-shoots - basic back-to-the-drawing-board stuff - or whether we're on track and just need a bit of honing and polishing."

A year and a half of honing, polishing and re-shooting later, the picture is finally ready for release, and Cleese is doing the promotional rounds of chat shows, looking about 10 years older for his trouble. The American audience reaction, it transpires, dipped badly in the last reel, and Casey Silver, Universal's chairman, suggested re-shooting the ending so as not to lose one of Kline's characters too prematurely. The re-writes were completed over a year ago, but the logistical problems in re-assembling the cast proved somewhat thornier, particularly since Michael Palin had disappeared off to the other side of the world to make Palin's Pacific, another of his popular globe-trotting TV series.

By the time all the principals had a vacant window in their schedule - late last August - Robert Young had started work on another film, so when Fred Schepisi called Cleese to enquire whether he'd like to play Don Quixote to Robin Williams's Sancho Panza - a big "yes", unsurprisingly - he turned the tables and asked the director to do the re-shoots. The scene which I had seen being shot wound up on the cutting-room floor; indeed, there is no helicopter in the finished film, and no animatronic rhino either. As for King, the lion - prematurely pounced on by the Conservative Party as a symbol of fearsome leadership - he was deemed too tame and written out. The music, too, is different from that envisioned 18 months earlier: the unusual pan-cultural soundtrack devised by John Du Prez and Peter Gabriel to reflect the zoo's ethnic diversity has been replaced by a more quotidian score from Jerry Goldsmith. All told, the film has been given a thorough overhaul, but despite everything, Cleese remains sanguine about the process, particularly with regard to comedy.

"It's the only way to do it," he insists. "Some people are surprised: Charlie Crichton (director of Wanda and various Ealing classics) told me that no audience ever saw an Ealing comedy before it was released. But I started as an actor, and I'd get up on stage at the Cambridge Footlights and we'd do a sketch one night, and afterwards go back to the clubroom and over our ginger beers, we'd say, 'Why didn't that line work?', and try it slightly differently the next night, until it worked. So the whole idea of trying something on an audience until you find what works is first nature to me. I don't think it's first nature to the kind of film people who think it's somehow corrupt or depraved to allow an audience to influence your vision of the film. If you're Kurosawa, you can think that way; the rest of them are just pompous oafs"n